The floods in Thailand have put prices through the roof.
If you see a bargain grab it.
Externals are easy enough to open up (plenty of youtube vids).
Just buy an extra SATA data and an extra SATA power cable (eg see amazon internal hdds and look at what customers 'also bought')
Note: even though HDDs have 2 or 3 yr warranty, you will invalidate by removing)
If you don't have SATA ports in Desktop you may need a SATA-IDE adapter (may come with cables)